U.S. patent number 4,118,632 [Application Number 05/735,787] was granted by the patent office on 1978-10-03 for nuclear medicine diagnostic instrument for the determination of the distribution pattern of a radioactive radiation source.
Invention is credited to Heribert Luig.
United States Patent |
4,118,632 |
Luig |
October 3, 1978 |
Nuclear medicine diagnostic instrument for the determination of the
distribution pattern of a radioactive radiation source
Abstract
The invention relates to a nuclear medical diagnostic instrument
for the determination of the distribution pattern of substances
emitting gamma quanta and inserted in a body, which consists
essentially of a detector with a localization arrangement and two
or more multi-channel collimator elements placed in front of the
detector.
Inventors: |
Luig; Heribert (34 Guttingen,
DE) |
Family
ID: |
5960173 |
Appl.
No.: |
05/735,787 |
Filed: |
October 26, 1976 |
Foreign Application Priority Data
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|
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Oct 27, 1975 [DE] |
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2547981 |
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Current U.S.
Class: |
250/363.1;
378/149; 378/150; 976/DIG.429 |
Current CPC
Class: |
G21K
1/025 (20130101) |
Current International
Class: |
G21K
1/02 (20060101); G21F 005/04 () |
Field of
Search: |
;256/505,511,512,513,514 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Borchelt; Archie R.
Claims
Having thus disclosed the invention, I claim:
1. A nuclear medicine diagnostic instrument for the determination
of the distribution pattern of gamma ray emission of radioactive
substances serving as a gamma ray source inserted into a body and
emitting gamma quanta, said instrument consisting essentially
of:
the combination of a detector and an adjustable collimator means,
said collimator means consisting of a plurality of multichannel
collimator elements placed between the source and said detector to
thereby form a distribution pattern for localizing said gamma
quanta from said source in the body;
said collimator elements being formed of perforated plates and
further comprising at least one moveable collimator element, said
elements lying on the source side of the collimator means and being
axially shiftable;
each of said plurality of collimator elements having its respective
channels in mutual alignment and coaxial alignment with a
neighboring channel in another collimator element to provide at
least a pair of coaxially aligned collimator elements in the array;
and
adjustment means including limiting means for maximum adjustment to
axially shift one of the said collimator elements relative to the
neighboring collimator element and to maintain alignment of the
elements whereby improvement in definition and sensitivity is
achieved in the pattern of radiation.
2. A nuclear medicine diagnostic instrument for the determination
of the distribution pattern of gamma ray emission of radioactive
substances serving as a gamma ray source inserted into a body and
emitting gamma quanta, said instrument consisting essentially
of:
the combination of a detector and an adjustable collimator means,
said collimator means consisting of a plurality of multichannel
collimator elements placed between the source and said detector to
thereby form a distribution pattern for localizing said gamma
quanta from said source in the body;
said collimator elements being formed of perforated plates and
further consisting of several moveable and relatively thin
collimator portions having a longer base on the detector side of
the perforated plate for a greater depth of bore on the detector
side than on the source side;
each of said plurality of collimator elements having its respective
channels in mutual alignment and coaxial alignment with a
neighboring channel in another collimator element to provide at
least a pair of coaxially aligned collimator elements in the array;
and
adjustment means including limiting means for maximum adjustment to
axially shift one of the said collimator elements relative to the
neighboring collimator element and to maintain alignment of the
elements whereby improvement in definition and sensitivity is
achieved in the pattern of the radiation.
3. A nuclear medicine diagnostic device as claimed in claim 1,
characterized in that said moveable collimator portions of said
moveable relatively thin collimator elements have channels which
consist of protruding casings which are attached to said perforated
carrying plate, and
said adjustment means further includes pushing means whereby the
casings can be pushed in the manner of a telescope into the
channels of the adjacent collimator element.
4. A nuclear medicine diagnostic device as claimed in claim 3,
characterized in that the combination of collimator elements and
adjustment means further includes two outside perforated plates
casings of substantially identical shape or one main surface of the
perforated plate and a middle perforated plate and a middle
perforated carrying plate which is provided with similarly shaped
casings protruding in both sides thereof, the outside diameter of
the middle casings being larger than the diameter of the casings of
the outside perforated plates.
5. A nuclear medicine diagnostic device as claimed in claim 4
including a spindle and guide bars for said shifting means said
guide bars guiding the moveable collimator elements without
protruding from the casings and said shifting means by adjustable
means of said spindle drive.
Description
FIELD OF THE INVENTION
This invention lies in the field of Nuclear Medicine and in
particular to a nuclear medicine diagnostic instrument for the
determination of the distribution pattern of a radioactive
radiation source.
DESCRIPTION OF THE PRIOR ART
For examining a living body for internal disturbances and
especially for growths or tumors, radioactive nuclides emitting
gamma rays (quanta) are incorporated within the body in carefully
controlled amounts and in the form of selected chemical compounds
containing these nuclides which participate in the normal
metabolism of the organs under examination or in the areas of such
organs to be investigated by this procedure. These compounds are
absorbed and are stored at the sites or the places of disturbance;
the radiation or quanta from these sites correspond to an increased
or decreased measure of the degree to which the compounds
participate in normal or abnormal metabolism. These storage places
thereby become sources of gamma radiation of increased--or of
intensively decreased radiating environment. The radiation
intensity characterizes the site. By detection and measurement and
by picture representation of the distribution pattern of the
radiation the sites of disturbance in the body or in a part of the
body that is to be examined can be accurately diagnosed. By
successive measurements and corresponding picture presentations of
the variable distribution radiation pattern, one can determine
among other things the function and the circulation of organs in
question and of the areas of tissue surrounding the organs.
With the known diagnostic instruments, a scintilligraphic
representation will be obtained whereby the radiologist is afforded
two different technical procedures, one being a detector-type
machine, the other being a camera-type machine.
In the detector apparatus the picture is given by a collimated
detector sensitive to the gamma quanta from the source and the
detector scans the patient by lines in accordance with the known
principle operation of the scintilligraphic scanner.
In the camera aparatus, the picture is framed by a fixed camera and
by a not moveable camera system which is known as a gamma camera.
In both known instruments a multi-channel collimator is employed
and it always precedes the detector. The collimator collimates the
isotropic radiation to provide substantially parallel rays with the
exception of a small solid angle, this small angle starting from a
radiation point source lying inside the living body that is being
examined. Accordingly, the detector can localize as a point source
the location of the source of radiation in a projected picture
which serves as a viewing screen in connection with the point
source localization arrangement.
The known collimators generally consist of a lead plate provided
with a plurality of channels or with a plurality of throughbores or
the collimator may consist of a grid having a plurality of openings
and being built up from lead lamellae. In the case of the known
scanner which comprises a long, extending conical heavy lead
structure as the collimator, this type of collimator is also called
a conical lead diaphragm.
In the known collimator structures above described, the expression
"collimator bore" is generally used as a collective term to embrace
all kinds of collimator openings or passages. Depending on the
geometrical form of the opening or passage and also depending
especially on the density of radiation passing through the bore and
on the length of the bore as well as on the width of the bore, the
known collimators have a characteristic permeability which is
recognized in the art and is called the "geometrical sensitivity of
the collimator." As a result of this geometric sensitivity, a
certain sharpness of the picture is achieved depending upon the
solid angle for which the collimator is radiation permeable. The
picture sharpness which is achieved equals that which can be
obtained for a radiation point source lying at a certain distance
from the site under examination. In this manner, a high degree of
sharpness of the picture, for example, a high geometric resolution
of a collimator is always obtained at the cost of the geometric
sensitivity, and this will be explained further later in more
detail in connection with the description and with the present
invention on the basis of the drawings.
THE PROBLEM SOLVED BY THE PRESENT INVENTION
A diagnostic instrument equipped with a certain collimator
consequently has a predetermined, unchangeable sharpness of the
picture and geometric sensitivity. Depending on the type of
investigation, often, however, a higher sharpness of the picture,
of in other cases a higher sensitivity is desired, which hitherto
had been taken into consideration by assigning geometrically
variable and exchangeable collimators to a diagnostic device. The
exchange of the relatively heavy collimator plates, however, is
very cumbersome and time-consuming and for these reasons generally
cannot be carried out during the course of an investigation. Beyond
that, the exchange of collimator plates merely permits a step by
step change of the sharpness of the picture and of the sensitivity
which is a time-consuming adjustment. In addition, in the case of
the scintilligraphic investigation, where the radiation intensity
changes in the area of investigation and thus also the requirements
of the sensitivity of the measuring arrangement during the
examination, an exchange of the collimator plates is often not
possible, since the changes take place in many cases too quickly to
permit such change and because the patient must of necessity
maintain his position fixed relative to the detector system during
the entire examination procedure.
OBJECT OF THE INVENTION
In accordance with the above, an object of the invention is based
on the task of creating a diagnostic device according to the
definition of the apparatus species in the case of which means for
adjusting the geometric sensitivity and the sharpness of the
picture will insure that these will be adjustable continuously and
easily during the examination operation.
Other and further objects will be seen from the summary, drawings
and more detailed description below.
SUMMARY OF THE INVENTION
According to the invention, this objective is achieved through the
critical factor that the collimator consists of two or more
multi-channel collimator elements, the channels of which are
mutually aligned coaxially and the further requirement that at
least one collimator element is shiftable axially in relation to
the other collimator element. In the case of such a collimator in
accordance with the invention the distance between the collimator
elements is added to the total length of the mutually aligned
channels to thereby provide an additional collimating effect, for
example, in the sense of the collimation achieved so that by
pushing apart the collimator elements, the effective length of the
channel is increased and thus the sharpness of the picture can be
increased, while inversely, by pushing the elements together, the
geometric sensitivity can be increased. According to one embodiment
of the invention, provision can be made that the collimator
elements are constructed as punched or perforated plates or in the
form of an open lattice in a manner known per se, and in that the
collimator consists of a basic collimator on the side of a detector
with a great depth of the bore and of several moveable, relatively
thin collimator elements so that the maximum adjusting distances of
these elements may be limited in such a way, that the collimator
will always remain exclusively permeable or open for certain
trajectories of the beam, which pass through the bores which are
aligned and mutually coaxial. This first type of embodiment is used
preferably in the case of collimators which require a great septum
thickness or wall thickness, since the maximally permissible
distance between the collimator elements which have been pushed
apart depends on the septum thickness as will be explained in
greater detail later on. In this group of moveable thin element
collimators belong, for example, such collimators as are required
for taking pictures with the higher energy gamma rays. This group
of collimators also includes those where the septum thickness is
not determined by the energy of the gamma ray used, but by some
other requirement for the collection of data at a limit of the
apparatus. Such data exists for example, in the case of a
gamma-ray-camera-detector, which consists of individual, small
detector elements. In the case of these detectors there frequently
is only a single bore in front of each detector element, so that
the distance between the axes of the bores is equal to the distance
between the centers of the individual detector elements. The
diameter of the bores is determined according to the desired
resolution capacity. The septum thickness resulting from the bore
distance and the bore diameter is frequently greater than necessary
for the absorption of penetrating gamma quanta and accordingly the
moveable thin element collimator of the first type is needed. For
the illustration of operation with low energy radiation sources,
E.gamma. < 250 keV, a second and different type of embodiment is
preferred according to the present invention. This second
embodiment is characterized in that, in the case of one or several
collimator elements, the channels consist of protruding casings
which are each attached on a perforated carrier plate, and which
can each be pushed into the channels of the adjacent collimator
elements in the manner of a telescope. In this case, the collimator
elements always with a larger diameter of the channel can be
disposed on the side of the detector whenever one wants to utilize
the graduated conical shape of the channels, resulting from the
telescopic structure, for an increase of the picture sharpness, or
vice versa, the collimator elements can be disposed with the always
larger diameter of the channel on the side facing away from the
detector whereby the graduated conical shape of the channels is
utilized for the increase of the geometrical sensitivity of the
total collimator. According to a special development, provision can
be made according to the invention that the collimator consists of
two outside perforated plates always carrying equal casings on a
main surface, and of a middle perforated carrying plate with
casings protruding on both sides, the outside diameter of which is
somewhat larger than the diameter of the casings of the outside
perforated plate. In the case of this form of embodiment, the
effective diameter remains the same on both sides of the collimator
independent of shifting of the collimator elements. According to a
further structural characteristic of the invention additional
adjustment and guiding means may be provided so that the moveable
collimator plates are guided without clearance on guide bars and
are adjustable by way of a spindle drive.
BRIEF DESCRIPTION OF THE DRAWING
The invention will be explained in more detail in the following
paragraphs on the basis of the drawings.
FIG. 1 shows a measuring head of a diagnostic device developed as a
gamma camera with a fixed and a shiftable collimator plate
according to a first embodiment of the invention;
FIG. 2 is a schematic diagram referred to for the explanation of
the geometric sensitivity and of the sharpness of a picture in a
collimator;
FIGS. 3 and 4 each are a schematic diagram for the explanation of
the dependence of the geometric sensitivity and sharpness of a
picture of a collimator on the length of its channels and the depth
of its bore;
FIGS. 5 and 6 show two schematic diagrams for the explanation of
the collimator conditions for two variable adjustments of the
collimator in the case of the embodiment according to FIG. 1;
FIGS. 7 and 8 show in simplified schematic and diagrammatic
presentation two embodiments of collimators which are predominantly
suitable for pictures with high energetic radiation sources:
FIG. 9 shows in schematic presentation and in top view a
full-walled collimator plate provided with bores of passage;
FIG. 10 shows in perspective, simplified presentation the middle
range of the bore of the collimator plate according to FIG. 9;
FIG. 11 shows in perspective presentation a second collimator plate
which can be inserted in the manner of a telescope into the
collimator plate according to FIGS. 9 and 10;
FIG. 12 shows a partial cut through a collimator consisting of the
two collimator plates according to the FIGS. 10 and 11;
FIG. 13 shows a collimator in a pulled out state consisting of
three collimator plates which can be pushed into one another in the
manner of a telescope;
FIG. 14 shows the collimator according to FIG. 13 in a pushed
together state;
FIG. 15 shows another embodiment of the collimator; and
FIG. 16 shows the collimator according to FIG. 14 in a pulled out
state.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows the measuring head of a nuclear medical, diagnostic
instrument with a detector 2 disposed in a window of a lead screen
1, made, for example, of NaJ (TL)-crystal. The radiation which is
to be examined with regard to a distribution pattern, hits the
detector through the channels of a collimator, whereby the
collimator in the case of the embodiment consists of two
multi-channel collimator plates 3,4, which have an identical
picture of channel holes aligned with one another. A localization
arrangement given altogether the position number 5 is series
connected to the detector 2, which localizes the detector areas hit
by the gamma radiation and which delivers the signals for
triggering an oscillograph via the outlets X.sup.+ X.sup.- Y.sup.+
Y.sup.-, the picture points of which are registered by a camera.
The collimator plate 4 is shiftable continuously in an axial
direction of the collimator plate channels 6,7 on guide bars 8 via,
for example, a spindle drive, as a result of which the geometric
sensitivity and sharpness of the picture is continuously changeable
during operation, which will still be explained in more detail
subsequently.
FIG. 2 illustrates schematically the collimation conditions in the
case of a single collimator plate 3 and explains the important
values for the geometry of the scintilligraphic pictures. These are
the collimator thickness or synonymously, the depth of bore t, the
diameter d of the channels and bores 6 and a distance a of the
source of radiation from the lower surface of the collimator 3.
Furthermore, the minimum septum thickness s is of importance, which
gives the thickness of the wall between the bores which can still
be penetrated with sufficiently little probability by the gamma
quanta of the used energy. An additional important value is the
density of bores, for example, the number of bores on a surface
unit which is a function of d and s. The higher the density of
bore, the greater will be the quanta yield and thus the
permeability of the collimator. The permeability of the collimator
is designated as the geometric sensitivity. In FIG. 2 the area of
the curve F presents a measure for the geometric sensitivity of the
collimator, whereas the half value width B of the surface enclosed
by the surface F represents a measure for the sharpness of picture
of the collimator. For a source of radiation S lying at a certain
distance a from the collimator 3, one collimator plate has a
certain and characteristic geometric sensitivity and a certain
sharpness of picture or sharpness of definition.
FIGS. 3 and 4 illustrate the dependence of the geometric
sensitivity and of the sharpness of definition of the collimator on
the depth of the bore. In the case of the collimator 31 according
to FIG. 3, the depth of bore t.sub.1 is twice as large as the depth
of bore t.sub.2 of the collimator 32, according to FIG. 4, while
otherwise the same geometric conditions are present. Because of the
greater depth of bore t.sub.1, the collimator is permeable still
only for a solid angle with the radius r.sub.1 for the source of
radiation S.sub.1, while the source of the radiation point S.sub.2
can irradiate the detector crystal through the collimator 31 at a
solid angle with about twice as large a radius r.sub.2.
Correspondingly, the point source S.sub.2 in a good approximation
irradiates the four-fold detector surface. The cut through the
local quantum distribution (curves F.sub.1, F.sub.2) of the quanta
striking the detector crystal, shows that approximately four times
as many quanta can be proven in the case of the same strength of
source and the same time of observation in the detector crystal of
the arrangement according to FIG. 4. In this case, it is valid
generally that the geometric sensitivity of a collimator decreases
with the square of its depth of bore t. The sharpness of definition
on the contrary measured on the width of the local quantum
distribution in the detector crystal increases with the depth of
bore.
FIGS. 5 and 6 explain for the embodiment according to FIG. 1 how
the geometric sensitivity and the sharpness of definition of the
collimator arrangement can be changed by changing the distance
between the two collimator plates 3 and 4. In FIG. 5 the two
collimator plates 3 and 4 are pushed directly against one another,
after which the collimator becomes permeable for a solid angle
.alpha. and the cross-section which is curve F.sub.3 as cut through
the local quantum distribution shows a high geometrical sensitivity
with a relatively slight decrease in the desired geometrical
resolution. In FIG. 5 the effective collimator depth t.sub.3 is the
sum of the depths of the bores of the two channels 6 and 7.
In FIG. 6, the two collimator plates 3 and 4 are pushed apart by a
distance of .DELTA.t, as a result of which the displacement
.DELTA.t, in view of the collimation conditions, is added to the
axial length of the channels 6 and 7, and a clearly enlarged
effective depth of bore t.sub.4 results as compared with t.sub.3.
The radiation source S irradiates in the manner shown in towards
the detector crystal right through the collimator at only a
relatively small solid angle .beta., which to be sure leads to a
decrease of the geometric sensitivity but on the other hand to a
substantial increase of the sharpness of definition.
The quantum distribution (curve F.sub.4), changed as compared to
FIG. 5, results in the position according to FIG. 6 not only as a
result of the enlargement of the effective depth of bore t.sub.4 by
.DELTA.t, but with a slight portion also as a result of the change
of the distance of the source of radiation S from the underside of
the collimator plate 7. A decrease of this distance will lead
additionally to an increase of the sharpness of definition, while
in that case the geometric sensitivity remains essentially
unchanged.
In the case of the embodiment of the variable collimator according
to FIGS. 1, 5, and 6, one must however note, that the possible
paths of the rays pass exclusively through bores aligned coaxially
with one another, since otherwise side rays will disturb the
picture in a sensitive manner. Such side rays are recorded, for
example, in FIG. 6 starting out from point S.sup.1.
In FIG. 6, the distance .DELTA.t between the two collimator plates
3, 4 is enlarged beyond the permissible measure. In order to avoid
such side rays, the formula relating to the problem is as
follows:
In this formula the maximum distance is .DELTA.t, on the right hand
side and s = septum thickness, d = diameter of bore, and b.sub.1 =
thickness of the collimator plate 3 which is closest to the
detector.
According to the preceding formula, (1) the maximum distance
between two collimator plates is proportional to the ratio between
the septum thickness s and the diameter of bore d. This last named
ratio in the case of low energy radiation sources is so small, that
the extension which can effectively be achieved in the case of a
collimator of only two plates amounts to only a fraction of the
length of the element close to the detector. In order to meet this
requirement for extension according to FIGS. 5 and 6, the
embodiment is provided and covers the case in which the extension
of the collimator is brought about by a small change of the free
distance between two adjacent collimator elements. This embodiment
of the invention is suitable predominantly for collimators which
require a relatively great septum thickness s. This is true, for
example, with collimators used for taking a picture with higher
energy gamma quanta.
For these cases of application in solution to the problem shown in
FIGS. 5 and 6 the collimator arrangement of the invention is
provided in accordance with FIGS. 7 and 8 consisting of a plurality
of elements. According to FIGS. 7 and 8, this need to assuredly
provide small displacement a unique collimator is shown. This
embodiment of collimator consists of a plurality of elements
according to the FIGS. 7 and 8 which have a longer base collimator
3a on the side of the detector and which have a larger number of
relatively thin moveable elements 4a, 4b, 4c, and possibly 4d than
in the embodiment of FIGS. 5 and 6. In this arrangement the
permissible maximum distance .DELTA.t.sub.1 max between the two
elements 3a and 4a is calculated according to the above mentioned
formula (1). The maximum permissible distance between the second
and the third element 4a and 4b is calculated according to the
formula
wherein b.sub.2 is the effective width of the collimator part
comprising the two first elements. The maximum permissible
distances between the additional elements can be calculated
analogously. These calculations are valid only on the assumption
that lead is impermeable for gamma quanta even in the smallest
thickness of a layer. Since in reality gamma rays penetrate certain
small thicknesses of lead, the maximum distances between the
individual collimator elements must be limited to somewhat smaller
values that will result from the preceding formula.
FIG. 8 shows a collimator built up of a basic collimator 3a and
four movable elements 4a, 4b, 4c, and 4d in the fully pulled out or
extended state. In the fully extended case consideration must be
given to the fact that the distances between the elements must be
decreased always by extensions k in view of the path p of
penetration into the lead layer.
In the case of the extension of variable collimators, the movement
of the elements must be run in a coordinated manner. This
coordination of the movement in an advantageous manner can be
achieved by selecting various spindles of variable pitch. By means
of suitable mechanical devices, care can be taken of the fact that
there will always be one pair of spindles which will move one
collimator element, while it serves as a guide for the remaining
collimator elements thereby preventing tilting or canting.
FIGS. 9 and 10 illustrate in a simplified schematic presentation a
collimator plate 9 which is made of a full disc in which are
provided numerous bores or channels 10. Six of these channels are
always disposed hexagonally around a central channel. For a picture
with a gamma quanta of 140 keV, a septum thickness of fractions of
1 millimeter will suffice. On a collimator surface with a radius of
about 12 cm, several thousand bores 10 are thus accommodated. FIG.
9 further illustrates the edge 11 of the attachment of the
collimator disc 9 in which the bores 12 are provided for the
reception of the guide bars 8 and furthermore in which they are
also provided bores 13 for the reception of restraining or stop
means on the terminal side of adjusting spindles.
The additional collimator plate 14 shown in FIG. 11, is assigned to
the collimator plate 9, which plate 14 consists of a flat carrying
plate 16 provided with holes 15 into which the holes of casings 17
are inserted at their lower ends. The outside diameter of the
casings 17 is somewhat smaller than the inside diameter of the
bores 10, so that the casings 17 can be pushed in the manner of a
telescope into the bores 10 of the collimator plate 9, as
illustrated in FIG. 12.
The carrying plate 16 of the collimator plate 14 is likewise
provided at its edge with a guide bore 18 for the reception of
guide bars and with guide bores 19 for the reception of the
adjusting spindles. In case of the embodiment according to FIG. 12,
the collimator plate 9 facing the detector crystal is disposed
fixedly, whereas the collimator plate 14 provided with the casings
17 is shifted in order to change the effective total depth of the
bores of passage on the guide bars.
In principle, the variable collimator can consist of a large
plurality of plates shiftable in relation to one another. An
embodiment is also practical in the case of which no full-walled
collimator plate 9 according to FIG. 9 is used, but in the case of
which all collimator plates consist of elements provided with
protruding casings. The FIGS. 13 and 14 illustrate such an
embodiment in the case of which three collimator elements 23, 24,
25 always provided with casings 20, 21, 22 have been provided the
casings of which can be pushed into one another in the manner of a
telescope. FIG. 13 shows the collimator element or their casings in
a pulled apart position, while in FIG. 14 the collimator elements
are pushed closely into one another.
FIGS. 15 and 16 show a collimator consisting of three elements
which can be pushed into one another in the manner of a telescope.
The two outside elements 26,27 are developed identically and always
consist of a perforated plate which carry casings 28, 29 on the
main surfaces facing each other and which are aligned with one
another. The middle element 30 consists of a carrier plate with
casings 301, 302 protruding on both sides, the diameter of which is
somewhat larger than the diameter of the casings 28, 29 so that the
parts can intermesh in the manner of a telescope and in the manner
shown. In the case of this embodiment the effective diameter of the
bore remains constant at both sides of the collimator independently
of the shifting of the elements. This collimator which only has
very thin septa and is suitable for making pictures with low energy
gamma quanta, for example, the 140 keV quanta of the 99.sub.tc m.
(Technetium)
The invention is not limited to collimators with the round bore as
shown in cross section, but in the same way be extended to variable
collimators with cross-section square, triangular cross section and
hexagonal bores. Likewise, the advantages of the invention can be
realized by the use of latticelike collimators which are built up
from lead lamellae.
From the above it is seen that the diagnostic instrument probably
consists of the combination of direct and localizing means for
gamma quanta from a source in the body which is a radioactive
source. The multi-channel collimator elements are placed in
alignment to permit an array collimator for accurate pattern
resolutions.
* * * * *